In recent years, hybrid vehicles (HEV), electric vehicles (EV) and fuel cell vehicles have been manufactured and sold in the aspects of the environmental effect and fuel consumption, and further development of these vehicles is being carried out. In such electric-powered vehicles, the use of chargeable-dischargeable power sources is essential. As for such power sources, secondary batteries such as lithium ion batteries and nickel hydride batteries, and electric double-layer capacitors are generally used. Among these, lithium ion secondary batteries are particularly preferable for used in electric-powered vehicles because of high energy density and high resistance to repeated charge and discharge, and various efforts toward development of such secondary batteries are being made. Here, when a secondary battery is used as a power source for driving a motor for use in the above-mentioned electric-powered vehicles, plural secondary batteries are required and connected in series in order to ensure high output power.
However, if the batteries are connected via connectors, output power decreases because of electric resistance of the connectors. In addition, the batteries including the connectors are at a disadvantage in terms of space. Thus, the connectors cause a decrease in output density and energy density of the batteries.
As for the measures to solve the above-mentioned problems, development of bipolar secondary batteries such as bipolar lithium ion secondary batteries is being carried out. Bipolar secondary batteries include a power generation element in which plural bipolar electrodes each provided with a positive electrode active material layer on one surface of a current collector and a negative electrode active material layer on the other surface of the current collector, are stacked on top of each other via electrolyte layers or separators.
The current collector used in such a bipolar secondary battery is preferably light and made from a material having high electric conductivity in order to ensure a larger output density. In view of this, there have been proposed current collectors (resin current collectors) using polymer materials to which electrically conductive materials are added. For example, Japanese Patent Unexamined Publication No. 2006-190649 discloses a resin current collector including a polymer material in which metal particles or carbon particles are added as an electrically conductive material.